A wide variety of engines, notably compression ignition diesel engines, have a tendency to generate undesired amounts of particulate matter such as soot and ash during operation. It has become almost universal to equip such engines with particulate filters to limit the extent to which soot particles, etc. are discharged during operation. A wide variety of designs for such filters are known, some of which have met with significant commercial success. One feature of all common filter designs on the market is that they tend to clog with trapped particulates over time. It is common for diesel particulate filters to become at least partially clogged with particulates after only a few hours of engine operation. Once particulates accumulate beyond a certain point, engine operation can become compromised.
To continue operating an engine or machine associated with a particulate filter which has become clogged, it is typically necessary to “regenerate” the filter. In other words, something must be done to remove the particulate matter clogging the filter, other than discharging the undesired material into the environment. Certain machines with an internal combustion engine have a duty cycle wherein the engine is operated at a relatively high power output, resulting in exhaust temperatures high enough to “burn off” the clogged particulates. Other machines having lower range duty cycles tend to predominately produce lower temperature exhaust which is rarely, if ever, sufficient to initiate combustion of accumulated particulate matter. Regardless of duty cycle, it is increasingly common to equip engine systems with some auxiliary means for regenerating their particulate filters when needed. One common strategy relies upon the application of auxiliary heat to combust the particulates trapped in the filter, so that the particulate material is consumed while the gaseous combustion products are discharged. Electric heaters, injection of fuel into the exhaust system upstream of the filter, and various other strategies are used for this purpose.
A relatively more recent strategy utilizes heat from the exhaust itself to raise the temperature of the particulate filter and the particulate matter trapped therein to a temperature sufficient to initiate combustion and consequent consumption of the particulate matter. A component known in the art as a variable geometry turbine has been used for this purpose. Variable geometry turbines typically include turbine vanes or movable walls whose position/orientation can be adjusted to restrict flow of exhaust gases through the turbine. As a result, the pressure and thus temperature of the exhaust gases can be increased to initiate combustion and enable burning off of particulate matter in the filter. Systems are also known wherein the air to fuel ratio of the mixture burned by the engine is enriched to increase the temperature of the exhaust gases for regeneration of an associated filter. Relying on either of these strategies has proven to have various drawbacks. On the one hand, adjusting the air to fuel ratio of the engine may be insufficient by itself to raise the temperature of exhaust gases sufficiently to combust particulate matter in the filter. On the other hand, use of the variable geometry turbine strategy alone may also be ineffective, and can cause pressures in and downstream of the engine to increase above that which certain engine systems are designed to accommodate.
U.S. Pat. No. 6,981,370 to Opris et al. is directed to a method and apparatus for regeneration of a particulate matter filter in an exhaust system. Opris et al. disclose an engine system and operating method wherein a throttle valve positioned upstream of the engine is partially closed to reduce the amount of air entering the engine cylinders. Reduction of air is stated to result in a richer fuel/air mixture which in turn increases exhaust gas temperatures. The throttle valve is controlled in cooperation with an “extended open duration” of an intake valve to reach a desired exhaust temperature for filter regeneration. While the strategy set forth by Opris et al. may work quite well, it can be desirable in other instances to regenerate a filter without relying upon use of a variable valve control strategy.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.